The embodiments described herein relate generally to electrical machines, and more particularly, to methods and systems for cooling electrical machines.
Some electrical machines, such as generators or motors, can have a rotor, a stationary stator and associated windings. The use of windings in some electrical machines can result in an increase in generated electromagnetic forces and an increase in flux densities within the machines. The power density of electrical machines, however, can be limited by the maximum operating temperature of the windings. The current density and thus the specific power of these machines can be increased, and the efficiency of the machine can also be increased by the use of coolers.
Conventional generators may include high power, forced-air cooling systems. Forced-air cooling systems, however, may include bulky, large and costly equipment such as, for example, blowers and/or refrigeration systems and/or multiple heat exchangers; i.e., a water-to-air heat exchanger to cool the blower air and an air-to-water heat exchanger to cool the water from the first heat exchanger. Besides sometimes being unwieldy and fault-prone, these components may not fit within operational housings such as, for example, nacelles of wind turbines.
Some generators may also include liquid cooling systems. Liquid cooling systems, however, may increase eddy current flow along the liquid cooling tubes which can decrease the efficiency of the generator. Moreover, some liquid cooling systems couple the cooling tubes to the coil former, which can be an inefficient arrangement for heat transfer, since the liquid cooling tubes are not coupled to the heat generating coil windings.